The field of the present invention relates to lighting apparatus such as may be particularly used for varying the intensity of light produced by a light source for use in motion picture photography such as film and video.
In a motion picture production, it is often advantageous to vary the amount of light on a subject. One such occurrence is when a subject is moved progressively closer to the camera and light source during filming. When employing an artificial light source, the intensity may be varied by changing the power input to the light such as through a rheostat. However as the light intensity is varied, the color quality or color temperature is also varied. Though such color change may not be perceptible to the human eye, color film is easily affected by color quality change.
U.S. Pat. No. 4,015,113 discloses a variable intensity light source in which light from a lighting element is directed against a reflector. The reflector has adjustable degrees of reflectivity being comprised of a plurality of rotatable cylindrical rollers, each roller having half of its surface coated with a black, nonreflective material. As the rollers are rotated, the intensity of light may be varied without changing color temperature. Other devices have included shutter elements interposed in the light path, the elements opening or closing to vary the amount of light transmitted or reflected.
The present inventors have disclosed in their application Ser. No. 07/887,276, U.S. Pat. No. 5,371,655, a lighting apparatus in which light emitted from a source is passed through an aperture and then through a section of a movable, neutral density filter. The filter is specially designed to have a variable density, continuously increasing from one side of the filter to the other. By changing the position of the filter, selectively placing higher or lower density sections in the light path, the intensity of the light emitted by the lighting apparatus is varied. The neutral density filter is selected to be generally color neutral so that the color temperature of the light passing therethrough remains unchanged. The present inventors have recognized that the darkest portion of the neutral density filter may not be sufficiently dark and may allow some light to pass therethrough.